Studies will be performed in which the synergistic or prophylactic effects of continuous darkness or cyclic light environments are evaluated with respect to membrane development and intense light induced visual cell damage in rod outer segment organelles and pigment epithelial tissue. The assessment of membrane development and visual cell damage will be correlated to the variables age and light environment as well as genetic differences in rats by determinations of membrane constitutents. Microanalytical measurements of rhodopsin and lipid content, class and fatty acid composition will be employed along with determinations of lipid peroxidative intermediates or products. Ratios of the major membrane lipid and protein components will be established to evaluate the physiological state of membranes. Experiments are planned to explore an apparent dichotomy in photoreceptor cell response to environmental light by utilizing normal rats and those afflicted with hereditary retinal degeneration, primarily between the ages of 16 and 40 days. Procedures will be developed to achieve the isolation of purified pigment epithelium from both strains of rat thereby permitting studies on photoreceptor cell membranes to be extended to those tissues. Extensive in vitro experiments are planned in an attempt to better understand and more reliably measure intermediates and products of light induced lipid peroxidation in ocular tissues. The application of in vitro studies to the measurement of in vivo light induced peroxidation in the retina is anticipated from the knowledge gained from in vitro studies and by the use of novel experimental approaches.